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Subject[PATCH 10/16] netconsole: introduce netconsole_mutex
Date
console_lock protects the target_list itself and setting and clearing
of its ->enabled flag; however, nothing protects the overall
enable/disable operations which we'll need to make netconsole
management more dynamic for the scheduled reliable transmission
support. Also, an earlier patch introduced a small race window where
dynamic console disable may compete against asynchronous disable
kicked off from netdevice_notifier.

This patch adds netconsole_mutex which protects all target
create/destroy and enable/disable operations. It also replaces
netconsole_target->mutex used by dynamic consoles. The above
mentioned race is removed by this change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Miller <davem@davemloft.net>
---
drivers/net/netconsole.c | 48 ++++++++++++++++++++++++++++--------------------
1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 57c02ab..f0ac9f6 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -75,10 +75,14 @@ __setup("netconsole=", option_setup);

/*
* Linked list of all configured targets. The list and each target's
- * enable/disable state are protected by console_lock.
+ * enable/disable state are protected by both netconsole_mutex and
+ * console_lock.
*/
static LIST_HEAD(target_list);

+/* protects target creation/destruction and enable/disable */
+static DEFINE_MUTEX(netconsole_mutex);
+
/**
* struct netconsole_target - Represents a configured netconsole target.
* @list: Links this target into the target_list.
@@ -106,7 +110,6 @@ struct netconsole_target {
#endif
bool enabled;
bool disable_scheduled;
- struct mutex mutex;
struct netpoll np;
};

@@ -184,7 +187,6 @@ static struct netconsole_target *alloc_netconsole_target(void)
strlcpy(nt->np.dev_name, "eth0", IFNAMSIZ);
nt->np.local_port = 6665;
nt->np.remote_port = 6666;
- mutex_init(&nt->mutex);
eth_broadcast_addr(nt->np.remote_mac);

return nt;
@@ -196,6 +198,8 @@ static struct netconsole_target *alloc_param_target(char *target_config)
int err = -ENOMEM;
struct netconsole_target *nt;

+ lockdep_assert_held(&netconsole_mutex);
+
nt = alloc_netconsole_target();
if (!nt)
goto fail;
@@ -573,10 +577,10 @@ static ssize_t netconsole_target_attr_store(struct config_item *item,
struct netconsole_target_attr *na =
container_of(attr, struct netconsole_target_attr, attr);

- mutex_lock(&nt->mutex);
+ mutex_lock(&netconsole_mutex);
if (na->store)
ret = na->store(nt, buf, count);
- mutex_unlock(&nt->mutex);
+ mutex_unlock(&netconsole_mutex);

return ret;
}
@@ -610,9 +614,11 @@ static struct config_item *make_netconsole_target(struct config_group *group,
config_item_init_type_name(&nt->item, name, &netconsole_target_type);

/* Adding, but it is disabled */
+ mutex_lock(&netconsole_mutex);
console_lock();
list_add(&nt->list, &target_list);
console_unlock();
+ mutex_unlock(&netconsole_mutex);

return &nt->item;
}
@@ -622,6 +628,7 @@ static void drop_netconsole_target(struct config_group *group,
{
struct netconsole_target *nt = to_target(item);

+ mutex_lock(&netconsole_mutex);
console_lock();
list_del(&nt->list);
console_unlock();
@@ -634,6 +641,7 @@ static void drop_netconsole_target(struct config_group *group,
netpoll_cleanup(&nt->np);

config_item_put(&nt->item);
+ mutex_unlock(&netconsole_mutex);
}

static struct configfs_group_operations netconsole_subsys_group_ops = {
@@ -662,6 +670,7 @@ static void netconsole_deferred_disable_work_fn(struct work_struct *work)
{
struct netconsole_target *nt, *to_disable;

+ mutex_lock(&netconsole_mutex);
repeat:
to_disable = NULL;
console_lock();
@@ -685,6 +694,8 @@ repeat:
netconsole_target_put(to_disable);
goto repeat;
}
+
+ mutex_unlock(&netconsole_mutex);
}

static DECLARE_WORK(netconsole_deferred_disable_work,
@@ -791,6 +802,8 @@ static int __init init_netconsole(void)
char *target_config;
char *input = config;

+ mutex_lock(&netconsole_mutex);
+
if (strnlen(input, MAX_PARAM_LENGTH)) {
while ((target_config = strsep(&input, ";"))) {
nt = alloc_param_target(target_config);
@@ -818,24 +831,21 @@ static int __init init_netconsole(void)
register_console(&netconsole);
pr_info("network logging started\n");

+ mutex_unlock(&netconsole_mutex);
return err;

undonotifier:
unregister_netdevice_notifier(&netconsole_netdev_notifier);
- cancel_work_sync(&netconsole_deferred_disable_work);
fail:
pr_err("cleaning up\n");

- /*
- * Remove all targets and destroy them (only targets created
- * from the boot/module option exist here). Skipping the console
- * lock is safe here.
- */
+ /* targets are already inactive, skipping the console lock is safe */
list_for_each_entry_safe(nt, tmp, &target_list, list) {
list_del(&nt->list);
free_param_target(nt);
}
-
+ mutex_unlock(&netconsole_mutex);
+ cancel_work_sync(&netconsole_deferred_disable_work);
return err;
}

@@ -843,22 +853,20 @@ static void __exit cleanup_netconsole(void)
{
struct netconsole_target *nt, *tmp;

+ mutex_lock(&netconsole_mutex);
+
unregister_console(&netconsole);
dynamic_netconsole_exit();
unregister_netdevice_notifier(&netconsole_netdev_notifier);
- cancel_work_sync(&netconsole_deferred_disable_work);

- /*
- * Targets created via configfs pin references on our module
- * and would first be rmdir(2)'ed from userspace. We reach
- * here only when they are already destroyed, and only those
- * created from the boot/module option are left, so remove and
- * destroy them. Skipping the console lock is safe here.
- */
+ /* targets are already inactive, skipping the console lock is safe */
list_for_each_entry_safe(nt, tmp, &target_list, list) {
list_del(&nt->list);
free_param_target(nt);
}
+
+ mutex_unlock(&netconsole_mutex);
+ cancel_work_sync(&netconsole_deferred_disable_work);
}

/*
--
2.1.0


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